The present invention relates to an electrophotographic photoconductor comprising an electroconductive support and a photoconductive layer comprising a particular azo pigment as charge generating layer which generates charge carries when exposed to light.
Conventionally, a variety of inorganic and organic electrophotographic photoconductors are known. As inorganic electrophotographic photoconductors, there are known, for instance, a selenium photoconductor, a selenium-alloy photoconductor, and a zinc oxide photoconductor which is prepared by sensitizing zinc oxide with a sensitizer pigment and dispersing the same in a binder resin. Furthermore, as a representative example of organic electrophotographic photoconductors, an electrophotographic photoconductor comprising a charge transporting complex of 2,4,7-trinitro-9-fluorenone and poly-N-vinylcarbazole is known.
However, while these electrophotographic photoconductors have many advantages over other conventional electrophotographic photoconductors, at the same time they have several shortcomings from the viewpoint of practical use.
For instance, a selenium photoconductor which is widely used at present has the shortcoming that its production is difficult and, accordingly, its production cost is high, and it is difficult to work into the form of a belt due to its poor flexibility. Furthermore, it is so vulnerable to heat and mechanical shock that it must be handled with the utmost care.
In contrast to this, the zinc oxide photoconductor is inexpensive since it can be produced more easily than the selenium photoconductor. Specifically, it can be produced by simply coating inexpensive zinc oxide particles on a support. However, it is poor in photosensitivity, surface smoothness, hardness, tensile strength and wear resistance. Therefore, it is not suitable for a photoconductor for use in plain paper copiers in which the photoconductor is used in quick repetition.
The photoconductor employing the aforementioned complex of 2,4,7-trinitro-9-fluorenone and poly-N-vinylcarbazole is also poor in photosensitivity and therefore not suitable for practical use, particularly for a high speed copying machine.
Recently, extensive studies have been done on the electrophotographic photoconductors of the above-mentioned types, in order to eliminate the above-described shortcomings of the conventional photoconductors. In particular, attention has focused on layered organic electrophotographic photoconductors, each comprising an electroconductive support, a charge generation layer comprising an organic pigment formed on the electroconductive support, and a charge transport layer comprising a charge transporting material formed on the charge generation layer, which are for use in plain paper copiers, since such layered organic photoconductors have high photosensitivity and stable charging properties. As a matter of fact, several types of layered electrophotographic photoconductors are being successfully used in practice. Examples of the layered electrophotographic photoconductors are as follows:
(1) A layered type electrophotographic photoconductor whose charge generation layer comprises a perylene derivative and whose charge transport layer comprises an oxadiazole derivative disclosed in U.S. Pat. No. 3,871,882.
(2) A layered type electrophotographic photoconductor whose charge generation layer comprises Chlorodiane Blue which is dispersed in an organic amine solution and coated on an electroconductive support and whose charge transfer layer comprises a pyrazoline derivative disclosed in Japanese Patent Publication No. 5542380.
(3) A layered type electrophotographic photoconductor whose charge generation layer comprises a distyrylbenzene type bisazo pigment dispersed in organic solvent and coated on an electroconductive support, and whose charge transport layer comprises a hydrazone compound disclosed in Japanese Laid-Open Patent Application No. 5584943.
As mentioned previously, these layered type electrophotographic photoconductors have many advantages over other electrophotographic photoconductors, but at the same time, they have various shortcomings.
Specifically, the electrophotographic photoconductor (1) employing a perylene derivative and an oxadiazole derivative presents no problem for use in an ordinary electrophotographic copying machine, but its photosensitivity is insufficient for use in a high speed electrophotographic copying machine. Furthermore, since the perylene derivative, which is a charge generating material and has the function of controlling the spectral sensitivity of the photoconductor, does not necessarily have spectral absorbance in the entire visible region, this photoconductor is not suitable for use in color copiers.
The electrophotographic photoconductor (2) employing Chlorodiane Blue and a pyrazoline derivative exhibits comparatively good photosensitivity. However, when preparing this photoconductor, an organic amine, for example, ethylene diamine, which is difficult to handle, is necessary as a coating solvent for forming the charge generation layer.
The electrophotographic photoconductor (3) employing a distyryl benzene type bisazo compound and a hydrazone compound have an advantage over other conventional electrophotographic photoconductors in that the charge generation layer can be prepared easily by coating a dispersion of the bisazo pigment on an electroconductive support. However, the photosensitivity of the photoconductor is too low to use as a photoconductor for high speed electrophotographic copying machine.
Furthermore, recently there is a demand for a photoconductor for use in laser printers, in particular for a highly sensitive photoconductor having a photosensitivity in a semiconductor laser wavelength region.
The above-mentioned photoconductors, however, have too low a photosensitivity to use in practice for semiconductor laser.